This project is a longitudinal study of the long-term behavioral and physiological effects of early maternal separation in pigtail (M. nemestrina) monkeys. Our major goals are to (1) determine if separation in infancy predisposes an organism to increased vulnerability (e.g. are they "at risk") to behavioral or physiological disorganization in response to separation and other stress as an adult, and (2) to complete the Biobehavioral Developmental Profile (BDP) for the pigtail monkey, so that we can use nonhuman primates as animal models of human psychopathology in a more comprehensive manner. The agitation-depression reaction that accompanies maternal separation in pigtail infants is one of the best available animal models of certain types of human depression. The depression reaction includes behavioral disturbances, and pronounced changes in heart rate, cardiac arrhytmias, body temperature, several types of EEG activity, and sleep patterns. Some of these physiological changes persist after reunion with the mother, suggesting relatively long-term separation-induced disturbances in several homeostatic regulatory systems. Behavioral changes following separation in Rhesus infants are also known to persist as long as two years following separation. In this research we will study 20 pigtail infants from age 15 months to 5 1/4 years. Half will have experienced a maternal separation in infancy, half will not have. All 20 subjects by 15 months of age will already have been studied extensively, both behaviorally and physiologically in another ongoing research project (MH 19514). In the first half of this 7-year project (funds requested herein), the animals will be followed behaviorally as they approach adulthood. In the second half (funds to be requested later) the animals will be reimplanted with multichannel biotelemetry systems and studied both physiologically and behaviorally. Normal behavioral development and physiological organization will be studied, as well as the ability of the animal to cope with a variety of normally occurring and experimentally induced stresses, including the stress of separation, as an adult.